It is an app, and works really well – Mileage Keeper Review

Just replying to those 1-star reviews - Mileage Keeper actually is an app, there is no need to go online. The link is just to the help page. In the app on the device, hit ‘+’ in the upper-right to add a vehicle. Tap on the vehicle and hit ‘+’ in the upper-right to add a refueling. It is really simple to use.
Review by nb192837465 on Mileage Keeper.